Subsea arrangements housing power equipment underwater, such as transformers or frequency converters, may comprise a vessel filled with insulation and/or cooling fluid to encounter for the high pressure due to deep water depth. During storing, submerging to sea bottom and operation of the arrangement, temperature and volume of the insulation and/or cooling fluid varies, whereby pressure compensation of the fluid is needed. This involves the use of a pressure compensator, which is in fluid connection with the vessel of the arrangement. The pressure compensator receives excess fluid when its temperature and volume increase, and returns the fluid back to the vessel when it cools down.
Leakage of seawater into the pressure compensator and/or into a main enclosure of the subsea arrangement is a serious risk as it may prevent the operation of the subsea arrangement or damage the same. In case of leakage, seawater will come in contact with the power equipment and cause a costly equipment failure.
One type of prior art solution for detecting a leakage in a pressure balanced oil filled enclosure is to visually inspect the compensator position by means of a remotely operated vehicle (ROV). If the compensator is not moving during pressure changes within the enclosure, this may be an indication of a leakage.
An alternative type of prior art solution for detecting a leakage is to monitor the compensator position by means of an optical sensor, proximity switches or a linear variable displacement transducer (LVDT).
U.S. Pat. No. 8,714,176 B2 discloses a protection system for a fluid compartment of variable volume. The protection system comprises a detection means for detecting when the volume of the fluid compartment is outside a predetermined acceptable limit. The detection means may comprise a proximity sensor.
EP 2925102 A1 discloses a method of detecting a failure in a pressure compensation system. A control unit may be adapted to determine the presence of a failure of first or second pressure compensators on the basis of a displacement measured with a first or second measuring unit. The first and second measuring units may comprise an inductive or an optical sensor to measure the displacement of the respective pressure compensator.